In a conventional personal computer system, a micro processor unit (MPU), a memory controller and a connector are mounted on a printed circuit board serving as a mother board, and a memory module, which is composed of plural dynamic random access memories (DRAMs) mounted on the printed circuit board, is inserted into the connector.
Each semiconductor chip forming a DRAM is packaged and transformed into the semiconductor device, which can be mounted on the printed circuit board, and the semiconductor device, so called the package, is mounted on the memory module printed circuit board, which is joined with the other printed circuit board serving as the mother board by means of the connector. In case that structural elements are mounted, the intervals of the adjacent conductors in various joining portions are in the order of sub micron meter in a semiconductor chip, 1000 .mu.m in the package, 500 .mu.m in joining portion in a printed circuit board and 1,270 .mu.m in joining by means of a connector. As mentioned in the above, each joining portion copes with demand by enlarging its dimension.
In case that high bit rate transmission with a clock signal of more than 500 MHZ, such as picture transmission, inequality in lengths of signal or control lines in a transmission line cannot be neglected, and noise is apt to superpose on a driving voltage and a clock signal on the signal line, as the length of the transmission line increases. Especially, the signal line is straight or bent in the transmission line on a mounting surface thereof, and inequality in the lengths of the signal lines is inevitable. Since the delay time of the signal is closely related to the length of the signal line, the signals simultaneously transmitting through the same transmission line reach the input terminals of a semiconductor chip at different times, because or inequality in the lengths of the signal lines. In such a case, timing of the operations of the transistors is disordered, which may cause the miss operations of the semiconductor chip.
Table 1 shows levels of mounting and joining technologies of a DRAM in a personal computer. In table 1, the level of processing technology of a semiconductor chip is regarded as "1" as a standard of comparison. In mounting process in a package, since easiness of mounting is regarded as important, the dimension of a joining portion is apt to be enlarged, hence an effect if electromagnetic wave incident thereon cannot be disregarded especially in case of a semiconductor device for high bit rate data processing.
TABLE 1 ______________________________________ LEVELS OF MOUNTING AND JOINING TECHNOLOGY OF DRAM IN PERSONAL COMPUTOR WIRING APPLIED PITCH MAGNIFI- ITEMS TECHNOLOGY (.mu.m) CATION ______________________________________ 1 MPU MEMORY FINE PROCESS- 0.5 1 CONTROLLER ING OF WAFER 2 CHIP-PACKAGE WIRE BONDING 100 200 JOINING 3 PACKAGE- SOLDER 500 1000 PRINTED RE-FLOW CIRCUlT BOARD JOINING 4 PRINTED PIN-SOLDER 1270 2520 CIRCUIT JOINING IN BOARD- APERTURE IN CONNECTOR PRINTED JOINING CIRCUIT BOARD 5 CONNECTOR- PLUG INSERTION 1270 2520 MEMORY INTO PIN BOARD JOINING CONNECTOR 6 MEMORY SOLDER BALL 750 1500 BOARD-PKG JOINING JOINING 7 PKG-CHIP Cu-Pb 100 200 JOINING DIRECT JOINING 8 HIGH SPEED MOST ADVAN- 0.25 0.5 MEMORY CHIP CED FINE PRO- CESSING TECHNOLOGY OF WAFER ______________________________________
In data and signal transmission between memories and a memory controller, it is indispensable to suppress noise. As mean for suppressing noise in data transmission between the memory controller and the memories, a rambus channel developed by Rambus Inc. is reported on Nikkei Electronics, p.31 to 32, No. 701, October, 1997. It is effective to directly mount a memory chip on the rambus channel in a way of face down as a method for making a wiring length of a package be zero.
In this case, however, although it is necessary to remove unacceptable chips in advance in accordance with aging, it is impossible on the basis of present technology level. Accordingly, a CSP (Chip Size Package) called a micro BGA (Ball Grid Array) is used as a small-sized package. This package is joined with a printed circuit board via solder balls. In this package, a wiring pattern, which is obtained by etching a Cu film stuck to a polyimide film, is used as means for electrically connecting bonding pads of a semiconductor chip with ball pads of the solder balls. In packages of all kinds, considerable process of fabrication is necessary, and material cost thereof becomes high.